Effect of Water Stress on Turgor Differences and C-Assimilate Movement in Phloem of Ecballium elaterium.

The effects of water stress on pressure differences and (14)C-assimilate translocation in sieve tubes of squirting cucumber Ecballium elaterium A. Rich were studied. Water stress was induced by transfer of plants from culture solution to a polyethylene glycol 6,000 solution having an osmotic potential of -18.2 atm. Sieve tube turgor, turgor differences between source and sink, and translocation rate were decreased. After 260 minutes of translocation, only 19% of the total fixed (14)CO(2) had moved out of the leaf, compared to the control value of 62% after the same period of time. The results suggest that water stress slows translocation by lowering sieve tube turgor differences, which are essential for the pressure flow mechanism of conduction.